This invention relates to a process for interpolating position dependent periodic electrical signals generated by a digital position or angle measuring device. The invention is particularly suited for use with photoelectric measuring devices.
Incremental measuring systems of the prior art typically generate a series of electronic pulses whose number represents a measure of the change in the position or the angle of rotation being measured. These pulses are summed in an electronic up-down counter, and the sum is converted to a measurement value which is displayed numerically as a digital value.
The resolution capacity of such measuring systems is limited by the grid spacing of the precision measuring scale used. Attempts have been made in the past to improve the resolution of the digital measurement in such incremental measuring systems, especially through electronic measures.
In one well-known interpolation apparatus the primary analog signals from the scanning unit of the measuring device are phase-shifted to one another. These analog signals are applied to a resistance chain that includes a series of adjustable potentiometers. By tapping the potentiometers there can be generated a plurality of secondary signals that lie between the primary signals and thereby make possible an interpolation. The device disclosed in Swiss Pat. No. 407,569 is one example of such an interpolation apparatus.
In practice, interpolation devices with resistance networks for generating secondary signals are generally unsuitable for high resolution interpolation. The electronic circuitry expenditure required for interpolation rises enormously as the resolution of the interpolation rises. As a consequence, the high cost of high precision interpolating devices of the foregoing type is a significant drawback in many applications.